Phthalocyanine compounds are highly stable 18 π-electron-conjugated macrocycles that exhibit intense, bright colors, and are represented by the following general formula:

Phthalocyanines, which include metal-phthalocyanine coordination compounds (i.e., M is an atom or atoms capable of bonding to the central cavity of a phthalocyanine molecule and can have the capability to attach axial ligands) and metal-free phthalocyanines (i.e., M is H), are frequently used as dyes or pigments in the textile and paper industries, and have also been used as chemical sensors, photodynamic cancer drugs, nonlinear optical materials, catalysts and liquid crystals.
Phthalocyanines may be formed upon heating a phthalic acid derivative, such as phthalic anhydride, phthalimide, phthalonitrile or o-cyanobenzamide, with a nitrogen source, such as urea, in cases where the phthalic acid derivative does not itself contain sufficient nitrogen. The synthesis of metal phthalocyanine coordination compounds additionally requires the presence of an appropriate metal derivative. Metal phthalocyanines are commonly synthesized following one of two methods. One common method utilizes either phthalimide or phthalic anhydride (as a precursor to phthalimide) as the starting material, while the other method starts with phthalonitrile. Both methods involve the simultaneous synthesis of the ligand with formation of the metal complex.
In general, to synthesize a metal phthalocyanine from phthalic anhydride, phthalic anhydride is heated with urea, a metal halide such as aluminum(III) chloride (AlCl3) and a small amount of a catalyst, such as a molybdenum compound, in a high-boiling solvent, with urea acting as the source of nitrogen. The presence of the catalyst is essential in these reactions to catalyze the formation of a key intermediate, 1-amino-3-iminoiso-indoline. The use of phthalic anhydride as the starting material in the synthesis of the metal phthalocyanine pigment chloroaluminum phthalocyanine is described in Huanshun et al., “Metal phthalocyanine solid phase synthesis,” Ranliao Yu Ranse 41(3):150-152 (2004); Chinese Patent No. CN101717401; Japanese Pub. Nos. JP 2003-176424, JP 2003-176423; Japanese Patent No. JP 4407097; and U.S. Pat. No. 6,826,001. These procedures all involve the use of catalytic quantities of molybdenum, typically ammonium molybdate, molybdic oxide, or another similar molybdenum compound.
The other method commonly used to synthesize metal phthalocyanines starts with phthalonitrile and involves heating the phthalonitrile to around 200° C. with a metal halide such as AlCl3, with or without a solvent. For example, a process to synthesize chloroaluminum phthalocyanine using C1-C10 alcohols, for example ethanol, as the solvent gave only 68% yield (RU 2164233), and a method that involves heating phthalonitrile in water at 180° C. in the presence of AlCl3 is described as violently vigorous and resulted in only a 70% yield (JP 62-158284). Much lower yields were obtained when the reaction also involved the use of ammonia. A complex of ammonia and aluminum chloride was allowed to form before heating with phthalonitrile, resulting in a 47% yield of the chloroaluminum phthalocyanine (JP 2000-1270885).
As an alternative to the two methods described above, metal phthalocyanines also can be prepared by substitution (i.e., transmetallation) reactions. For example, chloroaluminum phthalocyanine can be prepared from a different metal phthalocyanine, such as copper phthalocyanine. In these reactions, the metal (e.g., copper) is replaced with aluminum by heating copper phthalocyanine in molten AlCl3 and NaCl to 240° C. for six hours (EP 0 635 550 and U.S. Pat. No. 5,556,966). However, the final product may contain unreacted copper phthalocyanine, thus raising similar environmental concerns as the phthalocyanines prepared using metal catalysts.
It is well known that the shade of copper phthalocyanines varies according to the number of chlorine atoms present in the molecule. Thus, the blue shade of the non-chlorinated copper phthalocyanine changes to green-blue when 8 chlorine atoms are introduced and to a more intense green shade (“phthalocyanine green”) when 12 or more chlorine atoms are incorporated into the copper phthalocyanine molecule.
Chlorinated metal phthalocyanines have been produced by a variety of methods. Liquid halogenating agents include sulfuryl chloride and thionyl chloride. Such halogen agents as aluminum chloride are used in limited quantities, but the bulk of the reaction medium consists of the liquid halogenating agent. In other words, the halogenating agent is dependent upon to supply the liquid medium for the reaction.
A typical procedure for the preparation of phthalocyanine green uses large amounts of expensive reagents as solvents such as chlorosulfonic acid, which are then discarded after the reaction is complete. Such processes are expensive due both to the waste of the discarded solvent and to long reaction times required to make the chlorinated phthalocyanines.
Moser and Thomas, Phthalocyanine Compounds, pages 172-179, Reinhold Publishing Corporation, New York (1963), disclose the use of copper chloride as a catalyst for chlorinating copper phthalocyanine. However, it does not disclose the use of copper chloride in a process involving the reaction of the copper phthalocyanine with sulfuryl chloride.
U.S. Pat. No. 3,320,276 teaches that sulfuryl chloride will halogenate a metal-free phthalocyanine or a metal complex of phthalocyanine such as copper phthalocyanine without the addition of elemental halogen in the presence of aluminum chloride and/or aluminum bromide and, preferably, containing an alkali metal halide such as sodium chloride with sulfur monochloride present as a halogen carrier. However, this process requires the aluminum chloride or aluminum bromide be in the form of a fluid melt. This has many disadvantages since it requires means for heating and maintaining the aluminum chloride in a fluid state. Large quantities of the aluminum chloride are required in this process, for example, all the examples call for 100 parts of anhydrous aluminum chloride for 10 parts of copper phthalocyanine. Further, the hydrolyzed aluminum chloride (at the end of the reaction) is discarded and may contribute to effluent problems.
Generally, phthalocyanine has been industrially halogenated by a method in which phthalocyanine is halogenated while it is dissolved in a eutectic salt of aluminum chloride and sodium chloride or a method in which phthalocyanine is halogenated while it is dissolved in chlorosulfonic acid. In these methods, however, it is industrially difficult to recover the solvent, and as a result, a large amount of an acidic effluent is caused. For environmental protection, the effluent should be treated, and a large cost is required for the treatment. As a halogenation method using a recoverable solvent in order to cope with the above problem, there have been disclosed methods using a metal chloride as a solvent. For example, JP-A-52-29819 and U.S. Pat. No. 4,948,884 disclose a method of halogenating phthalocyanine in a titanium tetrachloride as a solvent.
A need exists for an efficient process for synthesizing minimally chlorinated phthalocyanine pigments and pigment compositions, such as minimally chlorinated metal phthalocyanine pigments, wherein the number of chlorine atoms is less than 4, and also minimally chlorinated copper phthalocyanine pigments, where the average number of chlorines in the pigment composition is 1, thereby minimizing negative environmental impact.